1. Field Of The Invention
The present invention relates to a scroll type fluid displacement apparatus, and more particularly, to an Oldham coupling mechanism for a scroll type refrigerant compressor used in an automotive air conditioning system.
2. Description Of The Prior Art
Oldham coupling mechanisms of scroll type fluid displacement apparatuses are well known in the art. For example, U.S. Pat. No. 4,655,696 issued to Utter discloses a basic construction of an Oldham coupling of scroll type fluid displacement apparatus. A scroll type fluid displacement apparatus generally comprises two scroll members each having a spiral element. The scroll members are maintained angularly and radially offset so that the spiral elements interfit to form a plurality of line contacts between the spiral curved surfaces and thereby seal off and define at least one pair of fluid pockets. In operation, the relative orbital motion of the two scroll members shifts the line contact along the spiral curved surfaces and, therefore, the volume of the fluid pockets changes. Because the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, the scroll type fluid displacement apparatus compresses, expands or pumps fluid. Oldham couplings are but one approach for preventing relative angular movement between the orbiting scroll and a fixed portion of the apparatus.
One such Oldham coupling mechanism is disclosed in Japan Utility Publication No. S62-66284. Referring to FIGS. 1 and 2, Oldham coupling mechanism comprises Oldham ring 59 having an opening 59a formed at the center thereof, and a fixed ring 58 fixed to the compressor housing. First end 59b of ring 59 slidably engages end surface 57c of orbiting scroll 57 and second end 59c of ring 59 slidably engages end surface 58b of fixed ring 58. First end 59b of ring 59 is subjected to the compression reaction forces generated during operation of the compressor. The compression reaction forces are transmitted through end 59c of ring 59 to fixed ring 58.
Boss 57a of orbiting scroll 57 is placed in opening 59a of Oldham ring 59. The outer diameter of boss 57a substantially corresponds to the width of opening 59a. Accordingly, boss 57a may move vertically, but not horizontally, relative to Oldham ring 59. Opening 59a is elliptical in shape. Boss 57a moves along the ellipse as shown in FIG. 2. Oldham ring 59, along with boss 57a positioned in opening 59a, slide horizontally within end surface 58c of fixed ring. The combined vertical movement of boss 57a in opening 59a along with horizontal movement along end surface 58c describes orbital movement of the orbiting scroll.
In this arrangement, first and second ends 59b and 59c of Oldham ring 59 support rust loads caused by the compression reaction forces of orbiting scroll 57, since the thickness of Oldham ring 59 is greater than the combined depth of wall 57b of orbiting scroll 57 and wall 58b of fixed ring 58. Accordingly, the first and second ends 59b, 59c must be designed with sufficient surface area to sustain the thrust loads without seizure. Such design criteria, however, inevitably increase the size and weight of the Oldham coupling. Furthermore, the movement of the orbiting scroll imparts an inertia force on the Oldham ring 59, resulting in vibration of Oldham ring 59. The magnitude of vibration increases in proportion to the weight of the Oldham ring 59. Consequently, competing design criteria, i.e., size of Oldham ring to sustain thrust load vs. increased vibration, often dictate a less than desirable compromise.
On the other hand, if the thickness of Oldham ring 59 is Less than the combined depth of wall 57b of orbiting scroll 57 and wall 58b of fixed ring 58, fixed ring 58 ends up supporting the thrust load as surface 58a of fixed ring 58 slidably contacts axial end surface 57d of orbiting scroll 57. This contacting area, however, is extremely small, and as a result is thus subject to seizure as well.
Furthermore, the axial end surface 58c of fixed ring 58 is formed by an expensive lathing manufacturing process.